Lead
A two-month-old infant has not yet received a single dose of whooping cough vaccine. The first DTaP dose is scheduled for two to three months of age — which means there is a gap before any protection takes effect. The problem is that Bordetella pertussis can reach the infant during that window.
The most common source is not another child. It is an adult — a parent or grandparent whose immunity has waned — who carries the infection as a prolonged cough and doesn't recognize it for what it is, sharing the same space as the newborn. In infants, the characteristic "whoop" may never appear; instead, the cough is followed by apnea. Infant pertussis carries a case fatality rate of 1–4% even in high-income countries [1].
The cocooning strategy addresses this directly: vaccinating the adults closest to the infant to build an immune buffer — a cocoon — around a child who cannot yet protect themselves. This article explains what makes pertussis unusual, and what family vaccination actually means in practice.
What Makes Pertussis Different
Bordetella pertussis infection unfolds in three stages.
Catarrhal: relating to inflammation of mucous membranes causing increased secretion; from the Greek for "flowing down" phase (1–2 weeks): Runny nose and a mild cough — indistinguishable from a common cold. This is when the infection is most transmissible.
Paroxysmal phase (2–6 weeks): Severe coughing fits, classically ending with the high-pitched inspiratory "whoop." In infants, however, typical whooping is often absent; instead, the cough may be followed by a pause in breathing — apnea: cessation of breathing lasting more than 20 seconds, or shorter if accompanied by color change or heart rate drop — that can be life-threatening.
Convalescent phase (weeks to months): Gradual improvement, but cough can persist for months. The name "hundred-day cough" reflects this prolonged course.
In adults, pertussis typically presents as a cough lasting more than two weeks with no striking features — which is why it often goes unrecognized. In infants, the same infection can cause severe illness requiring hospitalization and ICU-level care.
Why Immunity Fades
DTaP vaccine (diphtheria-tetanus-acellular pertussis) is part of the routine infant schedule in Japan, starting at two to three months of age. Protection is effective, but it does not last indefinitely. Both vaccine-induced and naturally acquired immunity are estimated to fall below protective levels within five to seven years [2].
This means adults who were vaccinated or infected in childhood are susceptible to pertussis again — unless they receive a booster. It explains why pertussis has resurged in many high-income countries [3], and why Japan saw increased reported cases in 2024 [4]. Children who follow the routine schedule gain some protection; the vulnerability is the early-infancy gap before the schedule is complete, when the closest adults may be the infectious source.
The Cocooning Strategy and Maternal Vaccination
Cocooning — giving Tdap (tetanus-diphtheria-acellular pertussis for adults) to parents, cohabitating grandparents, and regular caregivers before or shortly after birth — aims to reduce the likelihood that anyone in the newborn's inner circle is currently carrying pertussis.
More direct evidence comes from maternal vaccination during pregnancy. An observational study in England found that infants of mothers who received Tdap during pregnancy had a 91% lower risk of pertussis-related hospitalization [5]. The mechanism is transplacental antibody transfer: passage of maternal antibodies through the placenta into the fetal bloodstream, providing temporary newborn immunity: maternal antibodies cross to the fetus and provide early protection before the infant's own vaccination begins.
Tdap is effective as a pertussis booster even if the adult has previously received Td (tetanus-diphtheria) [6]. A parent who has not had a pertussis-containing vaccine for decades — who has "just been getting Td when needed" — may have no effective pertussis protection at all. That is a conversation worth having with a physician before the baby arrives, or immediately after.
What Families Can Do
Beyond vaccination, there are practical steps families can take.
- If an adult in the newborn's household has had a cough lasting more than two weeks, consider seeking evaluation for pertussis — it can be confirmed by PCR or serology.
- During the period before the infant's first DTaP dose is complete, minimizing close-contact exposure to anyone who may be coughing is a reasonable precaution.
- If an infant develops a color change around the mouth during a coughing episode, or breathing appears to stop, seek emergency care immediately. Apnea requires urgent response.
Tracking infant symptoms with timestamps — the frequency of coughing fits, any change in breathing pattern — gives a physician more to work with at a visit and may be the difference between a useful description and a vague one. Parents often find that what happened four days ago is hard to reconstruct accurately without a written note.
Summary
Pertussis is not a disease of the past. It circulates continuously, fueled by waning immunity in adults who were vaccinated or infected years ago. The highest-risk window is the very beginning of infancy, before the routine schedule offers protection. The cocooning strategy and maternal Tdap vaccination exist to close that gap. During the period when an infant cannot protect itself, the immune status of the surrounding adults matters directly.
References
- Cherry JD. Epidemic pertussis in 2012 — the resurgence of a vaccine-preventable disease. N Engl J Med. 2012;367(9):785–787. doi:10.1056/NEJMp1209051. PMID: 22931315.
- Wendelboe AM, Van Rie A, Salmaso S, Englund JA. Duration of immunity against pertussis after natural infection or vaccination. Pediatr Infect Dis J. 2005;24(5 Suppl):S58–61. doi:10.1097/01.inf.0000160914.59160.41. PMID: 15876927.
- Skoff TH, Hadler S, Hariri S. The epidemiology of nationally reported pertussis in the United States, 2000–2016. Clin Infect Dis. 2019;68(10):1634–1640. doi:10.1093/cid/ciy757. PMID: 30212798.
- National Institute of Infectious Diseases (Japan). Pertussis surveillance data. IASR. 2024.
- Amirthalingam G, Andrews N, Campbell H, et al. Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet. 2014;384(9953):1521–1528. doi:10.1016/S0140-6736(14)60686-3. PMID: 25037990.
- Gall SA, Myers J, Picicchero M. Maternal immunization with tetanus-diphtheria-pertussis vaccine. Am J Obstet Gynecol. 2011;204(4):334.e1–5. doi:10.1016/j.ajog.2010.11.024. PMID: 21186366.